The Boston Celtics claimed critical home-court advantage and a 3-2 series lead in the Eastern Conference Finals, earning a gritty 93-80 Game 5 win against the Miami Heat on Wednesday.

In all four quarters the Celtics held the Heat to 23 points or fewer, but the offensive side of the ball was also far from clicking early on.

The Heat led 19-17 at quarter-time and after winning the second frame 23-20, they held an incredibly low-scoring 42-37 lead at the long break.

In the first half, both teams shot under 39 per cent from the field and 26 per cent from three-point range, but the Heat were winning the physical battle on the boards, pulling in nine offensive rebounds to just two for the Celtics.

The two teams also combined for just six fast-break points in the first half, illustrating the slow, grinding pace of play as both defences locked in, forcing better ball and man movement.

Back in Game 1, also in Miami, the Heat who came out of the locker room for the third quarter and went on a rampage to swing that game, but this time the shoe was on the other foot.

The Celtics doubled up the Heat in the third period, winning it 32-16 as Jayson Tatum, Jaylen Brown and Al Horford found rhythm on the offensive end.

Boston led 69-58 after three quarters, and extended that lead to 23 points in the opening minutes of the final frame, as Brown knocked down three big triples.

After a first half where he was the subject of plenty of criticism for his loose ball handling – with four first-half turnovers – Brown made the difference after half-time, finishing with 25 points on 10-of-19 shooting and five-of-nine from long range. He also had no turnovers in the second half, and the biggest dunk of the game.

Jayson Tatum was also at his playmaking best, with 22 points on a mediocre seven-of-20 shooting, but he added 12 rebounds and nine assists, consistently creating opportunities for shooters off the dribble and showing advanced ability to make reads as play unfolded.

The real story of the Celtics' success was their ability to take away the three-point line for the Heat, though.

With Jimmy Butler's jump shots not falling – finishing with 13 points on four-of-18 shooting – Miami simply had no avenue to reliable outside scoring.

The Celtics' ability to chase hard over the top of screens and dribble hand-offs made life miserable for Max Strus and Duncan Robinson, taking away their catch-and-shoot opportunities and turning them into dribblers, far outside their comfort zones. 

Strus finished zero-of-nine from the field, missing all seven of his three-point attempts, while Robinson was four-of-12, including three-of-10 from long range. As a team, the Heat were just seven-of-45 (15 per cent) from beyond the arc.

Instead, the Celtics dared the Heat to beat them inside, banking on the stoutness of their terrific interior defensive duo of Horford and Robert Williams III. That pairing combined for 17 rebounds, five blocks, two steals and just one foul.

Game 6 will head back to Boston, meaning the first-seeded Heat need to win on the road to save their season and force a Game 7.